P1232: NON-INVASIVE MINIMAL RESIDUAL DISEASE ANALYSIS BY IMMUNOGLOBULIN GENE REARRANGEMENTS ON CIRCULATING TUMOR DNA PREDICTS THE OUTCOME OF PATIENTS WITH DIFFUSE LARGE B-CELL LYMPHOMA
Authors: Roberta Soscia, Giovanni Manfredi Assanto, Irene Della Starza, Riccardo Moia, Donatella Talotta, Vittorio Bellomarino, Teresa Bellissimo, Alice DI Rocco, Luigi Petrucci, Maurizio Martelli, Anna Rita Guarini, Gianluca Gaidano, Robin Foà, Ilaria Del Giudice
Journal: HemaSphere (2023)

Topic: 20. Lymphoma Biology & Translational Research Background: Diffuse large B-cell lymphoma (DLBCL) is a heterogeneous disease with genetic diversity and variable outcomes. The standard monitoring of DLBCL response to therapy relies on the estimation of tumor reduction by PET/CT scan. The analysis of clonal immunoglobulin (IG) gene rearrangements using a next-generation sequencing (NGS) approach could be a powerful tool to track minimal residual disease (MRD). In DLBCL, one major obstacle is the absence of circulating lymphoma cells. Circulating tumor DNA (ctDNA), released from lymphoma cells and easily accessible from peripheral blood (PB), might be the best analyte for MRD assessment and a potential tool to identify patients at high risk of recurrence. Aims: To identify in newly diagnosed DLBCL patients IG heavy (IGH) and kappa light (IGK) chain clonal gene rearrangements by NGS on formalin-fixed paraffin embedded (FFPE) lymph node (LN) biopsies and on ctDNA extracted from PB. To explore if tracking clonal IGH/IGK rearrangements by NGS on ctDNA samples during/after treatment can be a non-invasive tool to monitor MRD. To correlate the MRD results with radiologic disease assessment at an interim analysis (at interim) and at end of treatment (EOT). Methods: A multicenter cohort of 53 consecutive newly diagnosed DLBCL treated with R-CHOP was included in this study. NGS clonality testing was performed using the LymphoTrack assay (Invivoscribe Inc, San Diego, CA) for IGH (FR1/2/3) and IGK on genomic DNA from the LN biopsies and on ctDNA from PB samples. MRD was analyzed by tracing the disease-specific clonotypes in plasma samples collected at interim, at the EOT, at month +6, +12, +24 and at progression. Mann-Whitney and Student t-test were employed to compare continuous variables, χ2-test and Kaplan Meier were employed to assess progression risk. Results: At diagnosis, tumor-specific clonotypes were detected in 46/52 (88.5%) evaluable FFPE LN samples and in 41/46 (89%) ctDNA samples. Clonality identification rate on baseline ctDNA correlated with extra-nodal disease (p=0.03); a trend with disease stage was observed (p=0.09). At an interim time-point, ctDNA MRD was positive in 8 of the 26 (31%) so far evaluated cases and 67% of them subsequently relapsed; it was negative in 18 (69%) patients and 12% of them relapsed (p<0.0001) (Fig. 1A). MRD at interim allowed to better categorize the 16 cases in partial response by CT scan: 8 patients were MRD-negative and 2 relapsed, while 8 were MRD-positive and 5 relapsed (p=0.08) (Fig. 1B). At EOT, MRD was positive in 7/16 (44%) so far evaluated cases and all relapsed; only 1 had a positive PET/CT at EOT. MRD was negative in 9/16 (56%) cases and none has so far relapsed (p=0.001) (Fig. 1A); 2/9 showed a false-positive PET/CT result (Fig. 1B). Overall, at EOT MRD and PET/CT were concordant only in 50% of cases. Finally, MRD was detectable in ctDNA before clinical progression in all cases. After a median follow-up of 37 months (range 2-59), MRD negativity was predictive of progression-free survival both at interim and at EOT. A clonal shift was observed in 2 cases which led to relapse. Summary/Conclusion: In most DLBCL patients at diagnosis, ctDNA was suitable for IG-based biomarker identification by NGS and was comparable to diagnostic LN biopsies. ctDNA MRD evaluation both at interim and at EOT allowed to predict the outcome of DLBCL patients. ctDNA MRD can refine the CT/PET-CT-based response. The impact of ctDNA MRD detection on prognosis has to be validated in larger series of DLBCL patients, in order to explore the possibility of MRD-adapted therapies.Figure 1. The ctDNA MRD both at interim and at EOT is predictive of progression-free survival (A) and refines the partial response (PR) at interim CT and the complete response (CR) at EOT PET/CT (B). Keywords: ctDNA, Minimal residual disease (MRD), Immunoglobulin gene, DLBCL